This invention relates to high voltage planar semiconductor devices, and more specifically relates to a novel configuration for the silox layer to prevent polarization of the layer under the influence of high lateral electric fields across the surface of the device.
A popular glassy protective coating over the surface of a semiconductor device employs the use of silicon dioxide which is relatively heavily doped with phosphorus. This material has the desirable insulation characteristics of undoped silicon dioxide but also has the ability to reflow smoothly when heated to relatively low temperature, thereby to form an impervious glassy cover over the surface it covers.
Phosphorus-doped silicon oxide is hereinafter referred to as "silox". The silox may contain from about 2% by weight to about 10% by weight of phosphorus. The higher the concentration of the phosphorus in the silox, the more polarizable the material becomes.
When silox is used in an environment where high lateral electric fields are present as is the case in planar semiconductor devices, the highly speed silicon dioxide will polarize and tend to distort the field at the surface of the device and in the body of the device. Thus, in regions of critically high fields, the device is liable to fail as a result of added stress due to polarization of the silox in the area of high electric field stress.